The invention described herein was made by an employee of the United States Government and may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.
The present invention relates generally to the field of sensors and, in particular, to characterizing sensors.
Sensor characterization typically involves determining the sensitivity, noise threshold, frequency response, etc. of the sensor as well as sensor uniformity, e.g., variations in the sensitivity, noise threshold, frequency response, etc. as measured at different locations on a sensing surface or by several substantially identical sensors. Determination of sensor sensitivity, noise threshold, frequency response, etc. is also useful for sensor calibration. In situations involving sensors, such as highly sensitive microphones or other highly sensitive pressure sensors, for measuring small pressures, such as ultrasonic signals and audio frequency signals in air, sensor characterization and calibration is often difficult and painstaking.
For example, one method used for characterizing and calibrating sensors for measuring small pressures involves using a calibrated pressure sensor, e.g., calibrated using a standardized procedure at the U.S. National Institute of Standards and Technology, to calibrate a sound source for generating pressure waves in air at audio and ultrasonic frequencies. Calibration of the sound source involves exposing the calibrated pressure sensor to the sound source at various amplitudes and frequencies of sound and measuring an electrical output, e.g., voltage or current, of the calibrated sensor at each of the amplitudes and frequencies of sound. Then, an uncalibrated pressure sensor, e.g., substantially identical to the calibrated sensor, is exposed to the calibrated sound source at the various amplitudes and frequencies, and an electrical output of the uncalibrated sensor is compared to the electrical output of the calibrated sensor at each of the amplitudes and frequencies.
A number of problems are associated with using sound sources for characterizing and calibrating sensors. These problems include dispersion of the sound waves, echoes that may reach the sensor, and losses to the air in the case of ultrasonic sound waves. Moreover, few single sound sources have the bandwidth to cover the bandwidth required for characterizing and calibrating both audio and ultrasonic frequency sensors, so multiple sound sources are usually used for characterizing and calibrating both audio and ultrasonic frequency sensors. Further, sound sources are difficult to aim at specific locations on a sensing surface making it difficult to determine the sensitivity, noise threshold, frequency response, etc. at different locations on the sensing surface and thereby the uniformity of the sensing surface.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for apparatuses and methods for characterizing and calibrating sensors for measuring small pressures that do not employ sound sources for generating pressure waves.
The above-mentioned problems with using sound sources for generating pressure waves for characterizing and calibrating sensors for measuring small pressures and other problems are addressed by embodiments of the present invention and will be understood by reading and studying the following specification. Embodiments of the present invention provide apparatuses and methods that use light sources instead of sound sources for characterizing and calibrating sensors for measuring small pressures to mitigate many of the above-mentioned problems with using sound sources for generating pressure waves.
More particularly, in one embodiment, an apparatus for characterizing a pressure sensor is provided that has a light source for directing a beam of light on a sensing surface of the pressure sensor for exerting a force on the sensing surface. The pressure sensor generates an electrical signal indicative of the force exerted on the sensing surface. The apparatus has a modulator for modulating the beam of light at a plurality of frequencies and intensities. A signal processor is electrically coupled to the pressure sensor for receiving the electrical signal.
In another embodiment, a method for characterizing pressure sensors is provided. The method includes directing a modulated beam of light onto a sensing surface of the pressure sensor for exerting a force on the sensing surface. The method also includes generating an electrical output using the sensing surface indicative of the force exerted on the sensing surface.
In yet another embodiment, a method for calibrating a pressure sensor is provided that includes modulating a beam of light at a plurality of frequencies and intensities. The method also includes calibrating the beam of light so that the beam of light respectively exerts each of a plurality of known pressures on a sensing surface of the pressure sensor at each of the plurality of frequencies and intensities. Moreover, the method includes exposing the sensing surface of the pressure sensor to the beam of light so that the beam of light exerts each of the plurality of known pressures on the sensing surface. The method also includes generating respectively each of a plurality of electrical outputs using the sensing surface for each of the plurality of known pressures exerted on the sensing surface.